1. Field of the Invention
The present invention relates to optical systems. More specifically, the present invention relates to lightweight telescopes for helmet-mounted laser range finders.
2. Description of the Related Art
The next generation laser range finder (LRF) for the 21st century land warrior will be helmet-mounted such that the soldier can have both hands free for other mission critical tasks. A helmet-mounted laser range finder must be very lightweight and have a very low center of gravity. Otherwise, it would be very uncomfortable and unsafe to wear. Soldiers could easily break their necks during any accident.
The current hand-held LRF for soldier applications weighs about 1 lb, which is too heavy to be mounted on a helmet. A significant reduction in weight is required for helmet-mounted LRF applications. Additionally, the current LRF is expensive due to the required precision optical components.
A large contributor to the weight of the LRF is the telescope. Laser range finders require a telescope to transmit the out-going laser beam and collect the return signal. Conventional telescopes are based on refractive means such as lenses and mirrors. The optical power of a lens or mirror is proportional to its curvature, and requires a certain thickness to accommodate the curved surfaces. A refractive telescope is therefore very heavy in nature and unsuitable for the helmet-mounted LRF application.
Typical prior helmet-mounted displays (HMD) employed plastic lenses in an attempt to reduce the weight. A LRF with plastic lenses, however, would still be too heavy to be mounted on a helmet. Furthermore, the index of refraction of a plastic lens is very-sensitive to temperature and humidity changes. For HMD applications, any defocus due to index changes of the plastic lenses can generally be tolerated as long as it is within the human eye accommodation range. For LFR applications, however, any defocus error of the optics will introduce a beam divergence error. Consequently, the range of the LRF would be greatly reduced.
Hence, a need exists in the art for a compact, lightweight telescope suitable for helmet-mounted laser range finder applications.
The need in the art is addressed by the holographic telescope of the present invention. The novel invention is comprised of an eyepiece and a first holographic optical clement positioned to receive incident electromagnetic energy and focus the energy on the eyepiece. In the preferred embodiment, the eyepiece is a second holographic optical element, and both holographic optical elements are volume holograms. Each holographic optical element can be transmissive or reflective depending on packaging needs. The holographic telescope can be multi-spectral by including multiple independent holograms in each holographic optical element, each hologram responding only to a particular wavelength.